Advanced device assembly structures and methods

ABSTRACT

A microelectronic assembly includes a first substrate having a surface and a first conductive element and a second substrate having a surface and a second conductive element. The assembly further includes an electrically conductive alloy mass joined to the first and second conductive elements. First and second materials of the alloy mass each have a melting point lower than a melting point of the alloy. A concentration of the first material varies in concentration from a relatively higher amount at a location disposed toward the first conductive element to a relatively lower amount toward the second conductive element, and a concentration of the second material varies in concentration from a relatively higher amount at a location disposed toward the second conductive element to a relatively lower amount toward the first conductive element.

BACKGROUND OF THE INVENTION

Packaged microelectronic devices and related connection components, suchas interposers or the like, use various structures to facilitateattachment with other packaged microelectronic devices or connectioncomponents to form various microelectronic assemblies. Such structurescan include contact pads in the form of enlarged areas of a conductivemetal exposed at surfaces of the devices or components. Alternatively,such structures can be in the form of exposed ends of metalized vias,conductive pins, posts, or the like. When aligned with similarconnection features in another device or component, the connectionfeatures can be joined together using, for example, a conductive joiningmaterial, such as a solder mass or the like. Solder masses, such assolder mass 1 shown in FIG. 1A are often used to form such jointsbecause they can be easy to join between structures due to theirrelatively low melting temperature. Further, such conductive joiningmasses can be reworkable or reflowable, allowing repair or adjustment ofjoints.

The use of such joining masses can have some deficiencies, however, inparticular such joints, when melted in order to form joints between, forexample, contact pads or the like, can undergo lateral deformation. Thiscan be exhibited in widening of the masses prior to cooling, resultingin joints that are wider than the initially-deposited masses. Further,such widening can increase during normal use of the microelectronicassembly due to heating of the joints. As a result, as shown in FIG. 1C,it is generally accepted that a minimum spacing P between conductiveconnection elements, such as contact pads 2 (FIG. 1B) or the like, isequal to 1.5 times a width W of the conductive connection elements 2themselves. Further, because the widths of conductive joining masses,such as those of solder or the like, are directly related to the heightsthereof (due to surface tension during forming, which takes place in aliquid state), the higher a desired height of such a joint, the greaterthe width. This relationship can necessitate large contact pads 2 andlarge pitch P based solely on a desired bond height.

The need for relatively larger contact pads 2 or other connectionfeatures can result in increased dishing along bonding surfaces 3 ofthese features. In particular, when the surfaces of microelectronicdevices or connection components are finished by polishing (by chemicalor mechanical means), the connection features can develop a concavity.Such concavity can be increased in relatively larger features. Thisdishing can adversely affect bond strength and is generally notdesirable.

BRIEF SUMMARY OF THE INVENTION

An aspect of the present disclosure relates to a microelectronicassembly including a first substrate having a surface and a firstconductive element and a second substrate having a surface and a secondconductive element. The assembly further includes an electricallyconductive alloy mass joined to the first and second conductiveelements. The conductive alloy mass includes a first material, a secondmaterial, and a third material. The first and second materials each havemelting points that are lower than a melting point of the alloy. Aconcentration of the first material varies in concentration from arelatively higher amount at a location disposed toward the firstconductive element to a relatively lower amount toward the secondconductive element, and a concentration of the second material varies inconcentration from a relatively higher amount at a location disposedtoward the second conductive element to a relatively lower amount towardthe first conductive element. In an example, at least one of the firstor second substrates can be of at least one of a semiconductor materialor a dielectric material.

The alloy mass can have a thickness of less than 5 microns. In a furtherexample, the alloy mass has a thickness of less than one micron. Theconcentration of at least one of the first or second materials can varymonotonically from the relatively higher concentration to the relativelylower concentration. The location of the relatively higher concentrationof the first material can be adjacent the first conductive element.

The third material can include at least one of copper, nickel, bismuth,tungsten, cobalt, aluminum, tin, palladium, boron, gold, or silver or analloy of these materials and the like. Each of the first and secondmaterials can have a melting point of less than 200° Celsius in a stateunalloyed with the third material. In a further example, at least one ofthe first and second materials has a melting point of less than 50° C.in a state unalloyed with the third material. The first and secondmaterials can be low melting point materials. For example, the first andsecond materials can include different materials selected from tin,indium, and gallium.

In an example, the first conductive element can include a bulk conductormass with the conductive alloy mass overlying the bulk conductor mass. Aportion of the first material can be diffused into the bulk conductormass. In another example, the first conductive element can furtherinclude a barrier layer overlying the bulk conductor mass, and theconductive alloy mass can be joined with the barrier layer.

The first substrate can include a first support material layer of atleast one of semiconductor or dielectric material. In such an example,the support material layer can define the surface of the firstsubstrate, and the first conductive element can be a metalized viaextending through a portion of the first support material layer andbeing exposed at the first surface. The first conductive element candefine an end surface and an edge surface extending away from the endsurface, and a portion of the edge surface can contact the first supportmaterial layer within the via. Further, a portion of the edge surfacecan extend outside of the first support material. In such an example,the second substrate can include a second support material of at leastone of a semiconductor or dielectric material and defining the surfaceof the second element. The second conductive element can also bemetalized via extending through a portion of the second support materiallayer and being exposed at the surface, and at least a portion of theconductive alloy mass can be disposed within the second support materiallayer.

The first and second conductive elements can each have widths of lessthan 25 microns at respective bonding interfaces with the conductivealloy mass. In a further example, the first and second conductiveelements can each have widths of less than 3 microns at bondinginterfaces with the conductive alloy mass.

The first element can include a plurality of first conductive elements,and the second element can include a plurality of second conductiveelements. In such an example, a plurality of conductive alloy masses canbe joined between respective ones of the first conductive elements andthe second conductive elements. IN a further example, the firstconductive elements can each have a width, and the first conductiveelements can be respectively spaced apart from each other in a lateraldirection at a pitch that is less than the width of the first conductiveelements.

The first conductive element can include a plurality of capillarystructures extending in a direction towards the second element, and theconductive alloy mass can surround and be joined to at least someindividual capillary structures of the plurality of capillarystructures.

The first element can include a substrate defining the surface of thefirst element and extending in lateral directions, and the firstconductive element can be in the form of a post extending away from thesurface.

The first element can further include a microelectronic elementelectrically connected with the first conductive element.

Another aspect of the present disclosure relates to a microelectronicassembly that includes a first substrate defining a surface and a secondsubstrate defining a surface. The assembly also includes an alloy massjoined to the surfaces of the first and second elements. The alloy massincludes first, second, and third materials. A concentration of thefirst material varies concentration from a relatively higher amount at alocation disposed toward the first element to a relatively lower amounttoward the second element. A concentration of the second material variesin concentration from a relatively higher amount at a location disposedtoward the second element to a relatively lower amount toward the firstelement. A melting point of the alloy mass is greater than a meltingpoint of the first material in an unalloyed state and greater than amelting point of the second material in an unalloyed state.

In an example, the conductive alloy mass can surround an internal volumedefined between confronting portions of the surfaces of the first andsecond elements. Further, the internal volume is hermetically sealed.

In another example, the first and second elements can respectivelyinclude first and second conductive elements that define portions of thesurface of the first and second elements to which the conductive alloymasses are joined.

Another aspect of the present disclosure relates to a method for makinga microelectronic assembly. The method includes aligning a first bondcomponent with a second bond component such that the first and secondbond components are in contact with each other. The first bond componentis included in a first element having a substrate defining a surface anda first conductive element exposed at the surface. The first bondcomponent includes a first material layer adjacent the first conductiveelement and a first protective layer overlying the first material layer.The second bond component is included in a second element including asubstrate defining a surface and a second conductive element exposed atthe surface. The second bond component includes a second material layeradjacent the second conductive element and a second protective layeroverlying the first material layer. The method further includes heatingthe first and second bond components such that at least the first andsecond material layers diffuse together to form an alloy mass joiningthe first and second elements with one another.

The heating step can be carried out at a first temperature, and thealloy mass can have a melting point at a second temperature greater thanthe first temperature. The first and second protective layers candiffuse together and with the first and second material layers duringthe step of heating to further form the alloy mass. The step of heatingcan be carried out such that a temperature of the first and second bondcomponents reaches between 30° C. and 200° C. After the step of heating,the electrically conductive alloy mass can have a melting point ofbetween 200° C. and 800° C. In one example, the melting point of thealloy mass is greater than the melting points of either of the first orsecond material by at least 30 deg. C.

The first material layer can include at least one material component notpresent in the second material layer before the heating step. The firstand second protective layers can be of a similar composition. The firstmaterial layer and the second material layer can be low melting pointmaterials. In an example, the first and second low melting pointmaterials can be different materials selected from tin, indium, gallium,and/or their respective alloys. The first protective layer can includecopper, and the second protective layer can include at least one ofcopper, nickel, tungsten, cobalt, palladium, boron, gold, silver, and/ortheir respective alloys.

The first conductive element can include a bulk conductor layer and aseed layer that overlies the bulk conductor layer. The first bondcomponent can be joined to the seed layer. The method can furtherinclude controlling a melting point of the first material layer and thefirst protective layer, to which the temperature thereof can be raisedduring the heating step, by the thickness of the seed layer. The seedlayer can include copper. During the step of heating, the seed layer canalso diffuse with the first and second material layers. In a furtherexample, a portion of the first material layer can diffuse into the bulkconductor layer during heating. The first conductive element can includea barrier layer between the bulk conductor layer and the seed layer. Insuch an example, the barrier layer can prevent the first material fromdiffusing into the bulk conductor layer during the heating step. Thebarrier layer can include at least one of tantalum, tantalum nitride,molybdenum, chromium-molybdenum, nickel, phosphorous, tungsten, cobalt,palladium, titanium nitride, nickel phosphorus, cobalt phosphorus,titanium tungsten, nickel tungsten or combinations thereof.

The first substrate can be a first support material layer defining thesurface of the first element, and the first conductive element can be ametalized via extending through a portion of the first support materiallayer. In such an example, the method can further include forming thefirst bond component over the metalized via by depositing the firstmaterial layer within an opening of a resist layer that overlies thesurface of the first element, the opening being aligned with themetalized via. The step of forming the first bond component can furtherinclude depositing the first protective layer within the resist layeropening.

A seed layer can be positioned between the surface of the first elementand the resist layer prior to depositing the first material layer withinthe opening and can further overlie the end surface of the metalizedvia. Further, the first material layer can be deposited over the seedlayer within the opening, and the method can further include removingthe resist layer and portions of the seed layer that are uncovered bythe first material layer.

The first substrate can be a first support material layer defining thesurface of the first element, and the first conductive element can bewithin an opening within the first support material layer. In such anexample, an end surface of the first conductive element and the firstbond component can be recessed within the opening, and the step ofaligning the first bond component with the second bond component caninclude positioning the second bond component within the opening of thefirst support material layer. In a further example, the end surface ofthe first conductive element and the first bond component can berecessed within the hole such that an outer surface of the firstprotective layer is substantially co-planar with the surface of thefirst support material layer.

Another aspect of the present disclosure relates to a method for makinga microelectronic assembly. The method includes aligning a first bondcomponent exposed at a surface of a first element with a second bondcomponent exposed at a surface of a second element such that the firstand second bond components are in contact with each other. Each of thefirst and second elements includes a substrate, and the first bondcomponent includes a first material layer and a first protective layeroverlying the first material layer. The second bond component includes asecond material layer and a second protective layer overlying the secondmaterial layer. The method further includes heating the first and secondbond components such that at least the first and second material layersdiffuse together to form an alloy mass joining the first and secondelements with one another. The alloy mass has a melting point higherthan melting points of the first and second material layers prior toheating. The first and second protective layers can diffuse together andwith the first and second material layers during the step of heating tofurther form the alloy mass.

The first bond component can surround an area of the surface of thefirst element, and the second bond component can surround an area of thesurface of the second element. In such an example, aligning the firstbond component with the second bond component can define a volume withinthe first bond component, the second bond component, and the surroundedportions of the surfaces of the first and second elements. Further, thestep of heating can causes the internal volume to become hermeticallysealed by the conductive alloy mass.

The first and second elements can respectively include first and secondconductive elements that define portions of the surface of the first andsecond elements to which the bond components are joined, and the step ofheating can join the alloy mass between the first and second conductiveelements.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will be now described withreference to the appended drawings. It is appreciated that thesedrawings depict only some embodiments of the invention and are thereforenot to be considered limiting of its scope.

FIGS. 1A-1C show various structures in art related to the presentdisclosure;

FIG. 2 shows elements including corresponding bond portions prior tojoint formation in a method according to an aspect of the presentdisclosure;

FIG. 3 shows an alloy mass joining the elements of FIG. 2 according toan aspect of the present disclosure;

FIG. 4 shows exemplary concentration levels throughout the height of analloy joining mass;

FIG. 5 shows an element including a plurality of conductive elements andrelated alloy masses according to another aspect of the presentdisclosure;

FIGS. 6 and 7 show bond components that can be used to form an alloymass according to a method of the present disclosure;

FIGS. 8 and 9 show further steps in the alloy mass formation method;

FIGS. 10-15 show an element during various stages of a method for makingbond components according to an aspect of the disclosure;

FIG. 16 shows an assembly according to another aspect of the disclosurehaving alloy masses joining surfaces of adjacent substrates andconductive elements within each of the substrates;

FIG. 17 shows an assembly according to another aspect of the disclosurewherein bond portions can be used to form an alloy mass joining arecessed conductive element with a projecting conductive element;

FIGS. 18 and 19 show assemblies according to further aspects of thedisclosure that include combinations of the features of FIGS. 16 and 17;

FIGS. 20-24 show structures that can use bond components such as thosediscussed above with varying relationships between surfaces, conductiveelements, and the bond components; and

FIG. 25 shows a bond component over a conductive element withreinforcing structures therein.

DETAILED DESCRIPTION

Turning to the Figures, wherein similar numeric references are used inconnection with similar features, FIG. 3 shows a microelectronicassembly 10 according to an aspect of the present disclosure. Assembly10 includes first and second elements joined together by an alloy mass16. In FIG. 3, which shows alloy mass 16 joining the elements of FIG. 2,the first and second elements are shown as portions of microelectronicdevices, which can be in the form of packaged microelectronic elements,interposers, substrates, or the like. For example, first and secondelements 12 and 14 are shown in FIGS. 2-33 as including a supportmaterial layer 18 that can, for example be of a semiconductor or adielectric material layer such as found in an interposer structure, in aportion of a packaged microelectronic element, or in a portion of asemiconductor die. In an example, support material layer 18 can of oneof a semiconductor material, or of a dielectric material, or of acombination of semiconductor and dielectric materials, such as in theexample shown in FIGS. 2-3, wherein support material layer 18 includes asemiconductor layer 19 with a dielectric layer 20 overlying thesemiconductor layer 19. In such an example, dielectric layer 20 can beused to insulate routing or other conductive features formed on thesurface 28 of support material layer 18.

First and second elements 12, and 14 can include conductive elements,which can be traces, pads, posts, or the like. In the example shown inFIGS. 2-3, the conductive elements are metalized vias 22 that include abulk conductive mass 26 within an opening 23 in support material layer18 that is open to at least surface 28. In various examples, the opening48 can be a blind opening that terminates within the support materiallayer 18. In other examples, the opening 48 can be a through openingthat extends completely through support material layer 18. Further, inexamples where support material layer 18 includes a semiconductormaterial, an insulating layer can be included within opening 48 betweenthe bulk conductor layer 26 and the support material layer 18. Themetalized vias 22 can be structured such that the end surfaces 54 ofvias 22 are exposed at surface 28 of support material layer 18. As usedin this disclosure with reference to a substrate, a statement that anelectrically conductive element is “exposed at” a surface of a substrateindicates that, when the substrate is not assembled with any otherelement, the electrically conductive element is available for contactwith a theoretical point moving in a direction perpendicular to thesurface of the substrate toward the surface of the substrate fromoutside the substrate. Thus, a terminal or other conductive elementwhich is at a surface of a substrate may project from such surface; maybe flush with such surface; or may be recessed relative to such surfacein a hole or depression in the substrate.

For example, end surface 54 can be flush with surface 28, or recessedbelow surface 28. In another example the end surface 54 of the metalizedvia 22 can be positioned outside of surface 28 such that the edgesurface 56 is also exposed at surface 28 of support material layer.

As stated above, alloy mass 16 can be positioned between first element12 and second element 14 to join packages 12 and 14 together. In theexample shown in FIG. 3, alloy mass 16 is joined between confronting endsurfaces 54 of metalized vias 22. In such an example, alloy mass 16 canbe conductive such that the vias 22 are both mechanically andelectrically joined together such that an electronic signal or the likecan be transmitted from the first element 12 to the second element 14.This type of joining using alloy mass 16 can be used to connect a firstelement 12 in the form of, for example, a packaged microelectronicelement to a second element 14 in the form of an interposer or the likethat can further be electrically connected to a printed circuit board(“PCB”) or the like for use in an electronic device or as part of anelectronic system. In various examples, alloy mass 16 can have a heightH of between about 1000 Angstroms to about 2000 Angstroms, althoughgreater or lesser heights are also possible, depending on theconfiguration.

Alloy mass 16 can include at least three materials that vary in theirrespective concentrations throughout the structure of an individualalloy mass 16. As shown in FIG. 4, in an example, alloy mass 16 caninclude gallium (Ga), copper (Cu), and indium (In), and theconcentrations of these materials within the alloy material as a whole,can vary throughout the structure of alloy mass 16 at least in adirection between first element 12 and second element 14. As depicted inthe chart of FIG. 4, gallium can be present in an amount that varieswith the distance from first element 12 with a peak concentration level70 disposed toward element 12. In the particular example shown in thechart of FIG. 4, the peak concentration level 70 of gallium within alloymass 16 can be located at the point of attachment between alloy mass 16and via 22 of first element 12.

The concentration levels of all materials shown in FIG. 4 are exemplaryand can be influenced, for example, by the structure of the elements 12and 14 to which alloy mass 16 is connected. By way of illustration, theexample assembly 10 shown in FIG. 4 includes vias 22 that both includebarrier layers 32 between the bulk conductor layer 26 and alloy mass 16.The presence of barrier layers 32 can prevent any of the materialspresent in alloy mass 16 from diffusing into or otherwise becomingpresent within the bulk conductor layers 26. Accordingly, structureshaving no barrier layer may have different concentration levels atvarious locations throughout alloy mass 16, including around the bondinginterface between bulk conductor layer 26 and alloy mass 16. Even insuch an example, however, the peak concentration level of gallium may belocated within or at the bonding interface between the alloy mass 16 andthe bulk conductor layer 26.

Similarly, the concentration of indium within alloy mass 16 can be at apeak level 74 at a location generally disposed toward second element 14.Further, as discussed with respect to the concentration of gallium,above, the concentration profile of indium can deviate from thatdepicted in FIG. 4. For example, the concentration of Indium in thealloy may peak at a point closer to the first element 12. The profilemay depend on various factors, including processing temperatures,processing time, initial concentration profile, other processingconditions or depending on various structural factors of the assembly10, such as the presence or absence of a barrier layer, as discussedabove. Further, the materials included in alloy mass 16 can vary. Forexample, alloy mass can include a first material, that can be a lowmelting-point (“LMP”) material such as gallium, as discussed above. Ingeneral, such a LMP material has a melting point lower than about 250°C. and can include gallium, tin, indium, or the like. In some examples,such as that of FIG. 4, where the alloy mass 16 is joined betweenconductive vias, it may be preferable for the first material to be aconductive material.

Alloy mass 16 includes a second material that is also a LMP material,which may also be a conductive material, and can be selected from any ofthe above-listed LMP materials. In some examples, it may be preferablefor the first and second materials to be different LMP materials, suchas discussed above, where the first material is gallium, and the secondmaterial is indium. As discussed above, alloy mass 16 can include athird material, such as copper in the example of FIG. 4. The thirdmaterial can be a non-LMP material, such as one with a melting point ofgreater than about 160° C. In some examples, the third material can havea melting point of greater than 300° C. As with the first and secondmaterials, the third material can be a conductive material, especiallywhen used to join other conductive features together.

When the three materials are diffused together, such as in a mannersimilar to that illustrated in FIG. 4, the alloy mass 16 may have amelting point that is greater than either of the two LMP materials foundtherein. Further, the melting point of the alloy mass 16 can be lessthan 300° C. along at least a portion thereof such that the joint formedbetween the first and second elements 12 and 14 by alloy mass 16 can beat least partially “reworkable”. In an example, in a reworkable joint,alloy mass 16 can be at least partially reflowed by heating to atemperature of less than 300° C. such that at least a portion of alloymass 16 melts, allowing the position of elements 12 and 14 relative toeach other to be at least partially adjusted or further allowingelements 12 and 14 to be detached from each other.

As shown in the chart of FIG. 4, depending on the nature of a specificLMP material layer used, the LMP material may migrate away from asurface, such as end surface 54 of via 22, during the formation of thealloy mass 16. Accordingly, the peak concentration level of indium 74 isshown as being spaced away from the corresponding surface 54 of element14 with an increased level of copper therebelow. It is noted that insome examples, the peak concentration of indium may tend to invert withthe peak concentration of gallium. An increased thickness of theprotective layer 48 associated therewith can reduce the migration ofindium or similar materials and can prevent such inversion.

When the positions of the concentration peaks for the first and secondmaterials are described as being “disposed” toward either one of thefirst or second elements 12 or 14, such a peak can be closer to theelement 12 or 14 to which it is described as being disposed toward. Forexample, wherein the concentration peak 70 of gallium in FIG. 4 isdescribed as being disposed toward the first element 12, it can meanthat the peak 70 is closer to the first element 12 than the secondelement 14. Further, in such a convention, where the peak concentration74 of the second material, for example indium as illustrated in FIG. 4,is described as being disposed toward second element 14, it can meanthat such a peak 74 is closer to second element 14 than it is to firstelement 14. Alternatively, being disposed toward one or the other of theelements 12 or 14 can mean that such a peak is closer to such an element12 or 14 compared to the peak concentration of the other materials. Forexample, the peak concentration 70 of gallium can be considered asdisposed toward first element 12 in the example of FIG. 4, because it iscloser to first element than the peak concentration 74 of indium, andvice-versa.

Alternatively, whether a peak concentration of a material is disposedtoward an element 12 or 14 can be determined by whether such a peakconcentration is within a certain distance from the element, such as apercentage distance of the entire height of alloy mass 16. For example,the peak concentration 70 of gallium can be considered as disposedtoward first element 12 because it is within a distance of first element12 that is less than 50% of the distance between first element 12 andsecond element 14 (or the distance between the end surfaces 54 of thevias 22 of first element 12 and second element 14, respectively). Infurther examples, such a percentage distance can be less than 25%, orless than 10% of the total distance between elements 12 and 14.

As further shown in FIG. 4, the third, or non-LMP material can also havea peak concentration, such as the peak concentration 72 of copper shownin the graph of FIG. 4. As illustrated, the peak concentration 72 of thenon-LMP material can be positioned between the peak concentrations 70and 74 of the first and second LMP materials (gallium and indium,respectively in the example of FIG. 4). Accordingly, when determiningwhich element 12 or 14 a peak concentration 70 or 74 of a LMP materialis disposed toward in relative terms, such a peak concentration 70 or 74can be closer to such an element 12 or 14 than both the peakconcentration 74 or 70 of the other LMP material and the peakconcentration 72 of the non-LMP material.

The distribution and relative concentrations of materials within thealloy mass 16 can be influenced by the method by which alloy mass 16 isformed between elements 12 and 14. A method for making an alloy mass 16joined between and electrically connecting confronting end surface 54 ofmetalized vias 22 in a first element 12 and a second element 14 is shownin FIGS. 6-9, in accordance with an aspect of the present disclosure. InFIG. 6, a portion of a first element is shown having a metalized via 22at least partially through a support layer 18 and exposed at a surface28 thereof. A barrier layer 32 overlies a bulk conductor 26 within viaand, in this example, defines the end surface 54 of the metalized via22. As discussed above, the metalized via 22 can be without a barrierlayer such that the end surface 54 is defined by the bulk conductor 26.The bulk conductor can be of a conductive metal such as copper, nickel,tungsten, or various alloys including these or other suitable materials.The barrier layer 32, if present, can be of a material such as tantalumnitride (TaN), molybdenum, molybdenum-chromium, or the like. A seedlayer 34 can optionally be formed over barrier layer and/or the bulkconductor 26. The seed layer can be used to facilitate formation ofadditional layers over a barrier layer 32, for example, or over bulkconductors 26 of certain materials. The seed layer can also be used incontributing to various characteristics of the alloy mass 16 formed inthis or a similar method, as discussed below. In other instances, suchas when bulk conductor 26 is of copper and no barrier layer is present,a seed layer 34 may not be needed. Seed layer 34, if present, can be ofcopper or a similar conductive metal, and can be selected according tocriteria discussed below.

A first LMP material layer 36 overlies at least the bulk conductor 26with barrier layer 32 and/or seed layer 34, as discussed above,optionally positioned between bulk conductor 26 and the first LMPmaterial layer 36. The LMP material layer 36 can include any of the LMPmaterials listed above. LMP layer 36 can include a single LMP material,such as gallium, as in the example described above with respect to FIG.4, or in combination with another metal such as copper or the like. Forexample, LMP layer can be a single layer of gallium, a single layer of agallium-copper alloy, a single layer of a indium-gallium-copper alloy,or a structure having multiple sublayers of gallium and copper, or oneor more sublayers of gallium, copper, and indium or the like in apredetermined configuration to give LMP material layer 36 a desiredoverall percentage of the LMP material 36 that can also create a gradedconcentration level of the LMP material throughout the height of thelayer 36. As such LMP material layer may not itself have a “low” meltingpoint, as defined elsewhere herein, but can contain a desired amount ofone of the LMP materials discussed herein.

A first protective layer 38 can overlie the first LMP material layer 36and can include a similar material to that of bulk conductor 26, seedlayer 34, or any non LMP material included in LMP material layer 36. Inother examples, a selenium flash layer can be used for protective layer38. The protective layer 38 can provide protection for the LMP materiallayer 34 against oxidation or the like or against damage during handlingof element 12, for example. Protective layer can also provide at least aportion of a source of the non-LMP material within the finished alloymass 16, as discussed above with respect to FIG. 4. The thickness ofprotective layer 38, in particular the relative thickness with respectto LMP material layer and/or seed layer 34 can influence behavior of thebond portion 30 during subsequent steps of the alloy mass 16 formation,as discussed below. In an example, protective layer 38 can have athickness of about 200 Angstroms, although thicker or thinner protectivelayers can be used, depending on, for example, the criteria discussedabove. The various layers of first bond portion 30 or any other similarbond portions can be formed using electroplating, electroless plating,evaporation, chemical vapor deposition (“CVD”) or the like.

As with first bond portion 30, a second bond portion 40 can be joined toor otherwise connected with second element 14. In the example shown inFIG. 7, second bond portion 40 overlies an end surface 54 of a metalizedvia 22 through at least a portion of support material layer 18 of secondelement 14. Similar to first bond portion 30, second bond portion 40 canoptionally include a seed 44 layer that can overlie the bulk conductor25 of via 22, and via 22 can optionally include a barrier layer 42between seed layer 44 and bulk conductor 26. The barrier layer 42 andseed layer 44 can be of a similar construction and of similarcompositions to those discussed above with the barrier layer 32 and seedlayer 34 discussed above with respect to FIG. 6.

Second bond portion 40 further includes a LMP material layer 46overlying via 22 of second element 14 and further overlying barrierlayer 42 and seed layer 44, when present in the structure. LMP materiallayer 46 can include one of the LMP materials discussed above withrespect to FIG. 4 and can further include a different LMP material thanLMP material layer 36. For example, as illustrated in FIG. 4, LMPmaterial layer 46 can include indium. Further, LMP material layer 46 caninclude additional materials, such as a conductive metal such as copperor the like. Any additional non-LMP material within LMP material layer46 can be mixed with the LMP material in the form of an alloy or can beincluded in a number of sublayers to LMP material layer 46 that can beconfigured to provide a desired concentration of materials within layer46 and/or to provide a desired gradation of materials through athickness of layer 46, as discussed above.

As shown in FIG. 8, first element 12 and second element 14 can bepositioned such that the respective surfaces 29 confront each other andsuch that first bond portion 30 is aligned with second bond portion 40and are in contact with each other along the protective layers 38 and 48thereof. At least bond portions 30 and 40 can then be heated to apredetermined temperature to cause the LMP materials within therespective LMP material layers 36 and 46 to melt and to consume thenon-LMP materials found in any one of the protective layers 38 and 48,the seed layers 34 and 44, or within the LMP material layers 36 and 46themselves. During such heating, the alloy mass 16 can form as theconsumed non-LMP materials become solid particles suspended in a liquidphase of the LMP materials and as the liquid LMP materials mix together.Such a mixture will have a corresponding melting point for the mixtureas a whole that will vary according to the percentages (by weight or byatomic mass) of the components thereof, at which point the non-LMPmaterial will also melt into the mixture and the entire system will bein the liquid phase. Similarly, a LMP material, such as gallium, with alower melting point that another LMP material, such as indium, canconsume the other LMP material at a temperature above its melting point(30° C. in the example of gallium) but below the other LMP material'smelting point (about 156° C. for indium).

In some variations of bond portions 30 and 40 a protective layer 38 or48 may not be needed. For example, in variations of bond portions 30 and40 wherein the LMP material layer 36 includes a plurality of platedlayers in a pattern of LMP materials and non-LMP materials, theuppermost of such layers can be of a protective, non-LMP material, suchas copper. In other variations, the composition of the LMP materiallayers 35 or 46 can be graded alloy structures with at least enough of aprotective material near an upper portion thereof to negate the need fora separate protective layer 38 or 48. In this and possibly in othervariations (such as those wherein the protective layer is a volatilematerial that evaporates during heating), the materials of LMP materiallayer would not diffuse with any protective layer materials. In otherinstance, a protective layer may not be necessary, such as when thefirst and second elements 12 and 14 are formed and assembled in anenvironment with a low level of oxygen or are formed and assembledtogether before oxidization can take place.

Further, the amount of non-LMP material that can be consumed by theliquid LMP material varies with the temperature of the system. That is,the temperature required for consumption of the non-LMP material withinsuch a system increases as the amount of non-LMP material increases.Accordingly, the ratio of LMP material to non-LMP material within thebond portions 30 and 40 increases, the temperature required forconsumption of the protective layers 36 and 46 increases, whichaccordingly increases the temperature required for the separatematerials and components of the bond portions 30 and 40 to becomeadequately mixed to form alloy mass 16 that is joined to both firstelement 12 and second element 14. As shown in the exemplary diagram ofFIG. 4, the mixture does not need to be homogeneous to achieve alloymass 16 formation, but at least all of the protective layers 38 and 48should be consumed. In some examples the alloy mass 16 can be adequatelyformed after between 10 and 30 minutes of exposure to the proscribedtemperature. This can allow the materials within the alloy mass 16 to bemixed enough so that when cooled, the first and second elements will bejoined together and, in the case of the assembly 10 of FIG. 9, the vias22 of the respective elements 12 and 14 are electrically connectedtogether.

Because the temperature needed for alloy mass 16 formation increaseswith the amount of non-LMP material included within the bond portions 30and 40, this temperature, which can be referred to as the “bondingtemperature” can be controlled by the thicknesses of the protectivelayers 38 and 48 and any seed layers, such as seed layers 34 and 44,present in the bond portions 30 and 40. By selecting various materialsfrom those listed above and by adjusting the relative quantities of thevarious LMP materials and the non-LMP materials within the bond portions30 and 40, welding temperatures can be achieved within the range of 30°C. to 150° C. In the example discussed with respect to FIGS. 6-9,wherein the first LMP material layer 36 includes indium, the second LMPmaterial layer includes gallium, and the seed layers 34 and 44 as wellas the protective layers 38 and 44 are copper, the starting thickness ofthe seed layer may be 30-600 nm, the starting thickness of firstmaterial layer of gallium may be 100-500 nm, and the starting thicknessof the protective layer may be 10-100 nm. Similar thicknesses could beused for the second bond portion 40. In variations of the bond portions30 and 40 that include a non-LMP material within LMP material layer 36or 46, the proportion of such a non-LMP material to the LMP material canalso influence the bonding temperature of the bond portions 30 and 40.

The diffusion of the materials from the various layers of the bondportions 30 and 40 together into alloy mass results in a structure witha higher melting point than that of the LMP materials included therein,such as gallium and indium, as used in the example above. Further, oncealloy mass 16 cools and solidifies, the subsequent melting point thereofcan be higher than the welding temperature that was used in formationthereof. Various combinations of the materials listed above for thelayers within the bond portions 30 and 40 can result in bond portions 30and 40 with welding temperatures in the ranges given above that can formalloy masses 16 with melting temperatures also in the ranges givenabove. The particular welding temperatures of the bond portions andmelting temperatures of the resulting alloy masses 16 can be controlledor influenced by adjusting the relative proportions of the components ofthe bond portions 30 and 40 as discussed above. In other words, thenon-LMP material can be selected to increase the melting point of analloy including the non-LMP material and at least one other LMPmaterial.

The selective composition of bond portions 30 and 40 can be designed tocontrol the approximate welding temperatures thereof and the meltingtemperature of the resulting alloy mass 16 according to variouscriteria. For example, it may be desired to form alloy masses 16 thatare reworkable at temperatures that can be reached without causingdamage to other portions of the associated elements (such as elements 12or 14) or even without causing other bonds within the same package 10 orthe like to themselves become reworkable. Such criteria can be achievedwith a relatively higher LMP material to non-LMP material composition.Similarly, it may be desired for some bond portions that are used toform alloy masses to have a low welding temperature so that they can bemelted and joined together without causing already-formed joints orbonds to reflow or become damaged. On the other hand, it may be desiredfor some alloy masses 16 that are used to join elements together to havea relatively higher melting temperature so that they are more resistantto higher temperature applications or will not themselves reflow duringthe creation of subsequent alloy masses 16 or other joints in anassembly. Bond portions 30 and 40 can be made according to the abovecriteria to achieve these characteristics and to achieve suchcharacteristics in alloy masses 16 that they are used to form.

As discussed above, such alloy masses 16 can be used to join elementshaving a number of different microelectronic applications at variousfeatures thereof. In the example discussed above, alloy mass 16 is usedto electrically and mechanically join conductive vias 22 in an elementthat can be an interposer, a microelectronic die, a packagedmicroelectronic element, or the like. While only a single alloy mass 16is shown connected to corresponding metalized via 22 in each of thefirst element 12 and the second element 14, such an assembly 10 caninclude a plurality of metalized vias 22 in each of the first elementand the second element with corresponding alloy masses 16 attachedbetween respective ones of the plurality of vias 22. Such vias can bearranged in any number of configurations used in microelectronicassemblies or packaged microelectronic devices, such as in an array ofrows and columns of vias 22 spaced apart in, for example a minimum pitchor the like. Other features in similar arrays can be joined using alloymasses of the type discussed herein, such as contact pads connected withone or more other electrically conductive features such as traces or thelike or conductive pins or posts that can overlie and electricallyconnect with contact pads or the like.

In other applications, such features can be joined with masses of solderor other joining metals, which require a minimum pitch among the joinedfeatures of at least 1.5 times the width of that feature, as depicted inFIG. 1C. As illustrated in FIG. 5, bond portions 30 and 40 of the abovedescription can be used to join conductive features by formation of analloy mass 16 in applications where the conductive features are in anarray with a minimum pitch P that is less than the width of theconductive features themselves. Further, in assemblies with jointsbetween conductive features formed with masses of conductive joiningmaterial, such a solder, the bond height or spacing between elements canbe directly related to the width needed for such conductive features.That is, greater widths of the conductive features are necessitated bygreater bond height. In structures using the presently-described alloymasses 16 for joining of conductive features, such features can havewidths W of less than 6 μm, and in some cases, less than 3 μm, at bondheights greater than, for example 6 μm, although greater widths arepossible. The use of conductive features with decreased widths at theirrespective bonding interfaces can also result in structures that can bemore reliably made with less dishing at the interface surfaces of theconductive features. As shown in FIG. 1B, large contact pads 2 used inconnection with other joining structures can exhibit dishing (or theformation of a convexity) along surface 3 due to polishing or othersteps in the formation of such elements. This can result in decreasedjoint reliability, either during manufacture or use of such elements.

Bond portions 30 and 40 of the type discussed above in previous examplescan be formed on conductive features by a method illustrated in FIGS.10-15. In this specific example, bond portions 30 and 40 are shown asbeing formed over end surfaces 54 of conductive vias 22 at leastpartially through a support structure 18. Such elements can be made byforming holes in a semiconductor or dielectric layer, coating suchholes, if necessary, and by depositing a conductive metal therein. Suchholes can be blind and can originate through a surface opposite surface28. In such a method, the semiconductor layer 19 can be back ground andetched to expose the ends of the vias before depositing a dielectriclayer 20 over a semiconductor layer 19, which can be polished to exposethe end surfaces 54 of the metalized vias 22 to achieve the structureshown FIG. 10. Although only a single via 22 is shown in the package ofFIG. 10, multiple vias can be simultaneously formed in a package using asimilar method. Other methods of via formation can also be used.

As shown in FIG. 11, if a barrier layer 32,42 and/or seed layer 34,44are desired, layers 32′ and 34′ of the material desired for such layerscan be deposited over surface 28 of element 12. A resist layer 52 can bepositioned over surface 28 and over any bond material layer 32′ or seedmaterial layer 34′ present on element 12 and openings 50 can be formedor otherwise present in the resist layer 52 that overlie the vias 22 orany other locations where bond portions 30 are desired. The LMP materiallayer 36, according to any of the compositions discussed above, can bedeposited within opening 50, and then the protective layer 38 can bedeposited over LMP material layer 36. The resist layer 52 can then beremoved leaving the desired number of bond portions 30 on element 12 inthe desired locations. Subsequently, the portions of the bond materiallayer 32′ and seed material layer 34′ outside of the LMP material layer36 can be stripped away. A similar method can be used to make bondportions 40 on element 14, as shown in FIG. 15. The elements 12 and 14can then be aligned and heated to make alloy masses 16, as describedabove. Similar methods can be used to make similar bond portions onother conductive features, such as pads, posts, or the like.

Bond portions of the type discussed above to create alloy masses forbonding elements together can be used in variations of the elementsdiscussed above, such as that shown in FIG. 16, wherein additional alloymasses 116 are used to join support material layers 118 of packages 112and 114 together at portions of surface 28 that do not includeconductive features. As shown, some alloy masses 116 can be used in thesame package to join conductive elements, such as metalized vias 122,although in some applications, alloy masses 116 can be used to joinelements 112 and 114 along surface 128 only. The alloy masses 116 joinedto surface 128 can be made by the same method described above byincluding openings 50 within the resist layer 52 that do not overlie anyconductive features. In a further variation of that shown in FIG. 16,the alloy masses 116 can extend in one or more lateral directions alongsurfaces 128 such that the alloy masses 116 can define, along withconfronting portions of surfaces 128, an internal volume. In someapplications, a single, continuous alloy mass 116 of this type cancompletely enclose such an internal volume and, in a further example,hermetically seal such a volume.

As shown in FIG. 17, bond portions 230 and 240 similar to thosedescribed elsewhere above can overlie conductive vias 222 or otherfeatures that are recessed in one element 212 and project above surface228 in the other element 214. In a variation, via 222 of package 212 canbe flush with surface 228 and only bond portion 230 can project abovesurface 228, depending on the depth with which bond portion 240 isrecessed within the opening associated with via 222. In either form,such an arrangement can result in bond portions 230 and 240 that areself-aligning during assembly. Once the bond portions 230 and 240 arealigned, they can be fused, as discussed above to make alloy mass oralloy masses that joint the elements 212 and 214 together. Furthervariations of such an assembly are shown in FIGS. 18 and 19, in whichthe assembly 310 of FIG. 18 includes projecting and recessed vias 22, asin the example of FIG. 17 along with the surface bonded bond portions330 and 304 described with respect to FIG. 16. As shown in FIG. 19, suchbond portions 430 and 440 can further be used in an assembly 410including an edge chip structure 462.

Additionally, as shown in FIGS. 20-23, various different configurationsfor conductive features and related bond portions are possible withinthe framework discussed above, examples of which are shown in FIGS.20-24. As shown in FIG. 20, the end surface 524 of via 522 can berecessed below surface 528 such that the LMP material layer 536 or 546can also be positioned below surface 528 with protective layer 538 or548 being aligned with or flush with surface 528. In the example, ofFIG. 21, only a portion of LMP material layer 636 or 646 can bepositioned beneath surface 529, with the remainder projecting thereabovesuch that protective layer 538 or 548 is positioned above surface 528.FIG. 22 shows a variation of a bond portion 730 or 740 that can betapered along a portion of LMP material layer 736 or 746 such thatprotective layer 738 or 748 includes an apex 739 along a portionthereof. FIG. 23 shows a variation wherein a portion of the bulkconductor 826 projects above surface 828 with bond portion 830 or 840formed thereon and spaced above surface 828. Such a structure can beused to provide greater spacing between elements or to createself-aligning features, as discussed above with respect to FIG. 17. In afurther alternative example, FIG. 24 shows a bond portion 930 on aconductive post 962. Such a structure can be used to connect withanother bond portion joined to a conductive pad, another post, or thelike.

As shown in FIG. 25, either or both bond portions of the type discussedherein can include a reinforcing structure to help the bond portionretain its shape during welding or reflow, as discussed above. Inexample, a bond portion 1030 is shown on a bulk conductor of aconductive via 1022 in FIG. 25. A plurality of capillary structures 1058project from the end surface 1054 of the bulk conductor layer 1026 ofmetalized via 1022. The capillary structures 1058 can be of a flexiblematerial such as polyimide or the like and can be of a material that isheat resistant up to at least the intended welding temperature of thebond portion 1030. The capillary structures 1058 can be spaced apart onend surface 1054 such that the bond portion 1030 can make an adequateelectrical connection with the metalized via 22. Further, the capillarystructures 1058 can be of a sufficient size and density such that thesurface tension of the bond portion 1030, when melted, maintains thegeneral shaped desired for bond portion 1030 and a resulting alloy mass.Accordingly, bond portions 1030 can generally be formed that have higherbonding temperatures than those of bond portions of similar compositionswithout capillary elements. Any flexibility of capillary structures 1058can make the capillary structures resistant to breaking or the likeunder pressure between elements during assembly thereof. The capillarystructures 1058 can be formed by depositing a polyimide layer over aseed layer 1034 and then patterning the polyimide layer into the desiredshape and density of the capillary structures 1058 and to expose theseed layer. Further, the presence of the seed layer 1034 can minimizethe formation of intermetalic structures within the bulk conductor 1022.

Although the description herein has been made with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present disclosure as defined by the appended claims.

The invention claimed is:
 1. A microelectronic assembly, comprising: afirst substrate having a surface and a first conductive element; asecond substrate having a surface and a second conductive element; andan electrically conductive alloy mass joined to the first and secondconductive elements, wherein the conductive alloy mass includes a firstmaterial, a second material, and a third material, the third materialselected to increase the melting point of an alloy including the thirdmaterial and at least one of the first material or the second material,wherein a concentration of the first material varies from a relativelyhigher amount at a location disposed toward the first conductive elementto a relatively lower amount toward the second conductive element,wherein a concentration of the second material varies in concentrationfrom a relatively higher amount at a location disposed toward the secondconductive element to a relatively lower amount toward the firstconductive element, and wherein the third material has a highestconcentration at a location between a first highest concentration of thefirst material and a second highest concentration of the secondmaterial.
 2. The assembly of claim 1, wherein at least one of the firstor second substrates is of at least one of a semiconductor material or adielectric material.
 3. The assembly of claim 1, wherein the alloy masshas a thickness of less than five microns.
 4. The assembly of claim 1,wherein the concentration of at least one of the first or secondmaterials varies monotonically from the relatively higher concentrationto the relatively lower concentration.
 5. The assembly of claim 1,wherein the third material includes at least one of copper, nickel,tungsten, cobalt, phosphorous, palladium, boron, gold, or silver.
 6. Theassembly of claim 1, wherein the location of the relatively higherconcentration of the first material is adjacent the first conductiveelement.
 7. The assembly of claim 1, wherein each of the first andsecond materials has a melting point of less than 200° Celsius in astate unalloyed with the third material.
 8. The assembly of claim 7,wherein one of the first and second materials has a melting point ofless than 50° C.
 9. The assembly of claim 1, wherein the melting pointof the alloy formed with the third material and at least one of thefirst material or the second material has a melting point that is atleast 30° C. higher than the melting points of the first and secondmaterials.
 10. The assembly of claim 1, wherein the first material is adifferent material than the second material and the first and secondmaterials include materials at least one of tin, indium, or gallium. 11.The assembly of claim 1, wherein the first conductive element includes abulk conductor mass, the conductive alloy mass overlying the bulkconductor mass, and wherein a portion of the first material is diffusedinto the bulk conductor mass.
 12. The assembly of claim 11, wherein thefirst conductive element further includes a barrier layer overlying thebulk conductor mass, the conductive alloy mass bonded to the barrierlayer.
 13. The assembly of claim 1, wherein the first substrate includesa first support material layer of at least one of semiconductor ordielectric material, the support material layer defining the surface ofthe first substrate, and wherein the first conductive element is ametalized via extending through a portion of the first support materiallayer and being exposed at the first surface.
 14. The assembly of claim13, wherein a portion of the metalized via is positioned outside thefirst support material layer.
 15. The assembly of claim 14, wherein thesecond element includes a second support material of at least one of asemiconductor or dielectric material and layer defining the surface ofthe second element, wherein the second conductive element is a metalizedvia extending through a portion of the second support material layerwith at least a portion of the second element at the surface, andwherein at least a portion of the conductive alloy mass is disposedwithin the second support material layer.
 16. The assembly of claim 1,wherein the first and second conductive elements each have widths ofless than 25 microns at respective bonding interfaces with theconductive alloy mass.
 17. The assembly of claim 1, wherein the firstand second conductive elements each have widths of less than 3 micronsat respective bonding interfaces with the conductive alloy mass.
 18. Theassembly of claim 1, wherein the first conductive element includes aplurality of first conductive elements, the second conductive elementincludes a plurality of second conductive elements, and wherein aplurality of conductive alloy masses are joined between respective onesof the first conductive elements and the second conductive elements. 19.The assembly of claim 18, wherein the first conductive elements eachhave a width, and wherein the first conductive elements are respectivelyspaced apart from each other in a lateral direction at a pitch that isless than the width of the first conductive elements.
 20. The assemblyof claim 1, wherein the first conductive element includes a plurality ofcapillary structures extending in a direction towards the secondelement, the conductive alloy mass surrounding and being joined to atleast some individual capillary structures of the plurality of capillarystructures.
 21. The microelectronic assembly of claim 1, wherein thefirst element includes a substrate defining the surface of the firstelement and extending in lateral directions, the first conductiveelement being in the form of a post extending away from the surface. 22.The microelectronic assembly of claim 1, wherein the first elementfurther includes a microelectronic element electrically connected withthe first conductive element.
 23. A microelectronic assembly,comprising: a first substrate defining a surface and having a firstelement formed therein; a second substrate defining a surface and havinga second element formed therein; and an alloy mass joined to thesurfaces of the first and second elements, wherein the alloy massincludes first, second, and third materials, wherein a concentration ofthe first material varies concentration from a relatively higher amountat a location disposed toward the first element to a relatively loweramount toward the second element, wherein a concentration of the secondmaterial varies in concentration from a relatively higher amount at alocation disposed toward the second element to a relatively lower amounttoward the first element, wherein the third material has a highestconcentration at a location between a first highest concentration of thefirst material and a second highest concentration of the secondmaterial, and wherein a melting point of the alloy mass is greater thana melting point of the first material in an unalloyed state and greaterthan a melting point of the second material in an unalloyed state. 24.The assembly of claim 23, wherein the conductive alloy mass surrounds aninternal volume defined between confronting portions of the surfaces ofthe first and second elements.
 25. The assembly of claim 24, wherein theinternal volume is hermetically sealed.
 26. The assembly of claim 23,wherein the first and second elements respectively include first andsecond conductive elements that define portions of the surface of thefirst and second elements to which the conductive alloy mass is joined.